Area Under the Curve of Finger Photoplethysmography as an Evaluation Measure for Sympathetic Activity During Lumbar Epidural Anaesthesia.

Objective: To detect changes in finger photoplethysmography after administration of epidural anaesthesia as a surrogate method for evaluating autonomic nervous system activity.

Methods: We included a total of 46 patients scheduled for elective surgical procedures under lumbar epidural anaesthesia. A Biopac SS4LA pulse plethysmograph transducer was used for photoplethysmography recording, and the device was placed on the first toe of the right leg. The first standard lead of the electrocardiogram was simultaneously measured with the finger photoplethysmography. First measurement was done before the administration of epidural anaesthesia, and second measurement was done 25 minutes post administration of epidural anaesthesia.

Results: The area under the curve of the finger photoplethysmography statistically significantly increased 25 minutes after administration of epidural anaesthesia compared with the first measurement (p=0.0001). The amplitude of the finger photoplethysmography as well as the pulse transit time also statistically significantly increased after administration of epidural anaesthesia.

Conclusion: The area under the curve reflects the changes in sympathetic activity after epidural anaesthesia below the block level. It can be used for the detection of the degree of sympathetic block and, respectively, for epidural block success. Future prospects include detection of sympathetic block cessation as an indicator for discharge from the awakening room and beginning of patient verticalisation.